caltrap / caltrop ['kæltrǝp]
caltrap – n. – heraldry, a representation of a four-pronged device (at 120 degree angles), evenly spaced so that when three are on the ground the fourth points upward to injure or puncture
caltrop – n. – 1. a ball with four-prongs (at 120 degree angles), evenly spaced so that when three are on the ground the fourth points upward to injure or puncture; 2. puncture vine, of the genera Tribulus and Kallstroemia, with burrs or spiny bracts; 3. knapweed, Cenaurea calcitrapa, with purple flowers